Process for stretching polypropylene filaments



United States Patent PROCESS FOR STRETCHING POLYPROPYLENE FILAMENTS Robert E. Bierbaum and Emmett V. Martin, Kingsport,

Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Continuation-impart of abandoned application Ser. No. 649,004, Mar. 28, 1957. This application Aug. 17, 1961, Ser. No. 132,017

2 Claims. (Cl. 264-290) This invention relates to a method for producing polyolefin fibers having improved properties. More particularly this invention relates to a method of stretching polypropylene fibers which have substantially improved tenacity and modulus of elasticity.

This application is a continuation-in-part of our application Ser. No. 649,004, filed Mar. 28, 1957, now abandoned.

In recent years many types of synthetic fibers have been developed. These synthetic fibers as produced do not, a number of times, possess as good properties as may be desired in the fibers. Hence, a number of after-treatment methods and apparatus are described in the art for application to synthetic fibers for the improvement thereof. In general many of these after-treatments involve the application of heat to the fibers.

Numerous devices and media have been suggested for the application of heat as well as physical treatment of yarn. Among these are heated rolls and shoes, high frequency electromagnetic fields, heated liquids and heated gases and vapors. Unless the medium itself, such as a fluid, exerts a swelling or plasticizing action on the yarn, the type of heating medium employed ordinarily exerts little influence on the final properties of the yarn. Therefore, in the prior art the choice of methods of after-treatment has in many instances been made on the basis of convenience or economics.

Polyolefin fibers and yarns have been produced in recent years. While such polyolefin yarns are very resistant not only to water but different chemicals, and possess other useful properties, these polyolefin yarns have certain physical properties which are not as good as may be desired. Hence, it is apparent that the development of a method of treatment of such polyolefin yarns whereby the yarn can be improved, such as in its strength and elasticity, represents a highly desirable result.

After extended investigation we have found that polyolefin yarns, and in particular polypropylene yarn, somewhat in contrast to other synthetic yarns, react differently to different types of after-treatment and are particularly sensitive to a certain type of after-treatment. We have found that if polyolefin yarns of the class described herein are drawn in steam preferably super-heated steam as described in more detail hereinafter by a process employing relatively high draw ratios, that the properties of such polyolefin fibers and yarns are unexpectedly improved. This is unexpected because polyolefin yarns are quite hydrophobic and under ordinary circumstances have heretofore been regarded as little affected by water or water vapor. Use of steam rather than dry heat for the drawing medium results in greatly improved operation of the process. The yarns can be drawn at a greater rate of speed and with fewer broken filaments with use of steam. We have further found, in accordance with a more detailed embodiment of our invention, that if the steam-treated polyolefin yarn as just described is also given a heat treatment (heat-setting treatment) as will be described hereafter, that the yarn is still further improved. That is, by this latter step the polyolefin yarn is stabilized against shrinkage in boiling water.

The improvement obtained by treating polyolefin yarns ice with relatively high draw ratios and in steam in accordance with the present invention, and as will be set forth in detail hereinafter, appears to be considerably greater than can be obtained by after-treatments by other processes which might appear to be somewhat similar or comparable.

This invention has for one object the production of polyolefin fibers having improved properties. A particular object is to provide polypropylene and polyethylene fibers which have enhanced tenacity and modulus of elasticity. Still a further object is to provide a method of treating polyolefin yarns such as polypropylene yarn in a relatively simple, uncomplicated manner which will give improvements in the yarn in relatively few processing steps. Still another object is to provide a method for treating polyolefin yarns with superheated steam, and also in certain instances with heat-setting, which methods employ relatively high draw ratios and gives treated yarn having improved properties. Other objects will appear hereinafter.

As indicated above, in the broader aspects of our invention we have found that polyolefin yarns, even though they are normally quite hydrophobic and little affected by water or Water vapor, may be drawn at high draw ratios in a steam atmosphere, particularly a superheated steam. Such drawing at high draw ratios in such steam atmosphere quite unexpectedly permits obtaining yarns having a substantially greater strength and modulus of elasticity than may be accomplished by other types of treatment which may appear comparable. The polyolefin yarns of the present invention may be produced in various ways. These methods in their broader aspects comprise fluidizing polyolefin material such as by melting. Then the melted material is extruded through forming means such as spinnerettes to obtain the filaments, which filaments may be cooled in any conventional manner and wound up on yarn packages. For the purposes of illustration the following brief example will indicate how the polyolefin yarns employed in the present invention were prepared.

Five pounds of the polyolefin, in this instance polypropylene, were placed in the hopper of a melt extrusion apparatus. The polymer was vacuum dried. Following drying, an inert gas was introduced into the hopper to break the vacuum, and this inert atmosphere was then maintained above the polymer. The polypropylene used had a number-average molecular weight of about 75,000 and was of the type known generally in the trade as high molecular weight polypropylene. The hopper feeds into a heated screw mechanism of conventional construction. The polypropylene was heated to a temperature within the range of 200 to' 360 C. so that it was readily flowable. The fluid polypropylene was extruded under pressure between p.s.i.g. and 500 p.s.i.g. through a spinnerette nozzle having approximately 50 openings of circular configuration of a diameter of about 0.30 mm.

The polypropylene filaments emerging from the spinnerette were cooled in air by passing down a spinning column about 15 feet long. The cooled polypropylene filaments were gathered on a parallel package winder to form a yarn package containing aproximately 1600 yards (0.33 lbs.) of polypropylene.

While we have described the production of 600900 denier yarn containing about 50 filaments, other size yarn may be made in a similar manner. Likewise in a similar manner'and with similar apparatus polyethylene yarn may be produced.

The yarn produced as described above or by some other method, is then ready for an after-treatment in accordance with the present invention for improving its properties. It will be noted that the polyolefin yarn when treated by the present invention, is drawn at relatively high draw ratios, say a draw ratio in excess of four. The drawing equipment employed in the present invention consists of a feed roll. This roll is merely a means for withdrawing the end of the yarn from the yarn package and feeding it into the process. Means are provided for heating the yarn, usually referred to as drawing medium. This medium in accordance with the present invention is steam. However, it will be noted in the description which follows that reference will be made to employing either heated air or a heated roll in order to provide data for comparison with the use of steam in accordance with the present invention, from which it may be seen that operating with steam in accordance with the present invention gives improved results.

Finally, in the apparatus there is a draw or take-up roll. The yarn passes in the undrawn state from the yarn package to the feed roll from which the yarn is fed at a reasonably steady rate. The yarn then passes over or through the drawing medium which, as indicated in the present invention is steam. Then while the yarn is in a steam treated condition it is drawn many times its original length by means of the take-up or draw roll. The treated yarn from the draw roll is then repackaged in any convenient manner. As already mentioned, it will be noted from the present invention that the draw roll is operated at relatively high In the examples which follow the yarn feed speed was -30 feet per minute. The steam chamber used was approximately 24" long, supplied with steam at the desired rate through a preheater and a conventional pressure or flow regulating device. The yarn from the feed roll was threaded through a narrow slot on three sides of the steam chamber.

In the instance where the runs were carried out on a heated roll, the heated roll was a small internally heated metal roll which revolves with a surface speed equal to the yarn feed speed. The yarn was in contact with the heated roll for the various lengths specified in the runs. Roll temperature was measured by a surface temperature pyrometer.

In the runs where hot air was employed as the heating medium, the hot air chamber was made from a 2" diameter cylindrical rod about 18 long. An axial slot /3 wide and 1" deep was cut in the rod. The yarn ran through this slot. The rod was heated by electrical cartridge type heaters. The temperature listed in the runs is the temperature of the rod which is an approximate measure of the air temperature.

With the above description of apparatus in mind, attention may now be turned to the following examples:

EXAMPLE I.-EXAMPLES OF DRAWING CRYSTALLINE POLYPROPYLENE EXAMPLE II.-EXAMPLES OF DRAWING llIGII DENSITY POLYETIIYLENE Run Draw Tenacity, Elongation, Modulus of N 0. Drawing medium ratio g./den. percent elasticity,

gJden.

1 Steam at 105 C 18. 0 5. S5 5 144 Heated roll at 0., 2% in. 7.6 3.83 18 40 contact. 3 Heated roll at 105 0., 2% in. 8. 0 4. 17 53 contact. 4 Heated roll at (3., in. 8. 00 4. 05 17 18 con 5 11?}; air, chamber temp. 7. 40 3. 52 10 43 6 H231. air, chamber temp. 129 7. 72 4. 52 .21 41 EXAMPLE III 6 11%; air, chamber temp. 134

speed compared with the feed roll in order that a somewhat higher draw ratio is applied to the polyolefin yarn undergoing treatment by the steam process of the present invention.

The present invention will be further understood from the following examples which will be set forth. In these examples it will be noted that the first runs are illustrations of treatment in accordance with the present invention. Certain of the other runs are illustrations of prior art methods such as rather than using steam using hot air, heated rolls, etc. From these other runs it is possible to compare the results and observe the improvement obtained by the method of the present invention which employs steam.

In the above examples draw ratio means the number obtained by dividing the surface speed of the draw roll by the surface speed of the feed roll. The tenacity, elongation, and modulus of elasticity were measured on a standard Instron tensile tester with an elongation rate of 100% per minute. The modulus of elasticity isthe slope of the initial straight portion of the stress-strain curve, expressed in grams per denier per unit extension.

It is believed apparent from the preceding examples that it can be seen by using the relatively high draw ratios of 4 and in some instances above 8, in combination with steam that the properties of the polyolefin yarn are considerably improved over properties obtained by other methods of comparable simplicity and economy. For polypropylene yarn we would generally prefer steam at be- While we have described in particular the treatment of tween 120 C. and 165 C. In general superheated steam 50 filament 600900 denier yarn in the above examples, is preferred for all types of polyolefin yarn, but saturated our invention may be applied to other sizes of yarn which steam can also be used. are useful in the textile industry. The composition of the From the foregoing it will be seen that we have shown a 5 above yarns was substantially 100% polyolefin. We regard method for improving the tenacity and modulus of yarns it as surprising that a polyolefin yarn which will absorb consisting of polypropylene and polyethylene. We have practically no water, will respond in such a striking fashfurther found that there may be coupled with the treation, as set forth above, to the use of steam as a medium ment which has been described above a heat-setting step for drawing. However, polyolefin yarns of slightly modiwhereby the polyolefins of the class indicated may be 10 fied compositions can be similarly treated. For example, stabilized against shrinkage in boiling water. polyolefin yarns containing relatively small amounts of In further detail, this stabilization against boiling water modifiers such as dyes, pigments, ultraviolet inhibitors, shrinkage can be accomplished by heat-setting the polyantioxidants, plasticizers, fillers, and even copolymerizaolefin yarn in hot air on a heated roll or shoe or in steam. ble compounds to an extent of in most cases not more The yarn can be held at constant length or allowed to 1 than 5% and in no case more than 10% by weight of the shrink during the treatment. polyolefin can be processed in a comparable manner to For polypropylene yarn we have found the range of obtain improved yarn products. The number-average temperatures useful for this heat-setting purpose is from molecular weight of the polyolefin will usually be above about 90 C. to 140 C. and the time from 5 seconds to 5,000 and below 200,000, and preferably will be within 5 minutes. Temperatures below 90 C. are substantially the range of 10,000 to 50,000.

inelfective and the use of temperatures above 140 C. may The invention has been described in considerable detail result in the filaments adhering to each other and the loss with particular reference to certain preferred embodiof properties. Treatment for times less than 5 seconds merits thereof, but it will be understood that variations and produces rather little effect and the use of times longer modification can be effected within the spirit and scope of than 5 minutes appears to be unnecessary. the invention as described hereinabove, and as defined m In the case of the high density polyethylene yarns, the the appended claims. greferecrl1 temperature rfartrige is from about590 C. to 120 \lVeAclaim: f 1 1 fil an t e time range om 5 seconds to minutes. process or treating po ypropy ene amentary This embodiment of our invention pertaining to heatmaterial having a molecular weight of at least 5,000 and setting will be further illustrated by the several examples including: which follow: drawing said filamentary material to at least four times EXAMPLE IV.EXAMPLE OF HEAT-SETTING POLYPRO- its original drawn length in an atmosphere of PYLENE YARN IN HOT AIR WHILE HELD AT ooNsTANT steam at a temperature of at least about 100 C.; and LENGTH thereafter T t T. T Shrinkage in heat-setting said filamentary material in a hot gaseous fi a lme gg g atmosphere at a temperature of from between about cell: 120 C. and the melting point of said filamentary 6 36 5 material. g9 33 g 2. A process in accordance with claim 1 wherein steam :5 40 is superheated and is at a temperature of at least about 6.0 2 120 C. 35 References Cited EXAMPLE V.EXAMPLE OF HEAT-SETTDIG HIGH assesses IN HOT 11R WHILE 2 360 5 UNITED STATES PATENTS 45 ,3 2 10/1944 Lodge 8-151.2 shrinkage in CO1 et a1 Temperature, Time T(en71:i)ty Elongatiion, lgoiling 2,437,263 3/ 1948 Manning 264-210 X g. P010611 W3 :htper- K e 195 Elvin et a1. if, 3 2;; 2,584,043 1/1952 Oberley. 2. 2 1 2,622,961 12/1952 Finlayson et al. 4: 6 23 :7 BCSSOm. 23 2,664,010 12/ 1953 Emerson. XAIV VI MP H 3,173,977 3/1965 Es'selmann et al. 264210 E IPLE .EXA LE 0F EAT-SETTING POLYPRO- PYLENE YARN IN HOT AIR WITHOUT CONSTRAINT iifiggg 51322 5 53; :2 35x 2 Marilee-setting 2,420,565 5/1947 Rugeley et a]: 1.11:: 2s 1 Tempeii- Time hfiat- T t Elongashignliage 2,821,457 1/1958 ich 28-1 se, eaci, I (gt/(1.)" Pei-a2... wait 3 333 333 3; gggg 3 g;

percen M 36 8 5 2,289,860 7/1942 Babcock 264232 4.9 40 0:7 2,390,132 12/1945 Smith et al. 28-1 2:3 g 8 2,596,128 5/1952 Chavannes et al 264--290 3.0 60 0 2,679,450 5/1954 Hampson et al 264-206 EXAMPLE VII- XAMPLE or HEAT-SETTING HIGH 2934400 4/1960 slggel et 264-210 i giii s x L E 1fi%YENE YARN 1N HOT AIR OTHER REFERENCES g gz {fleet-setting Hand-book of Chemistry and Physics, 39th ed., pub. by Tem err- Time heat- T Etlongashr rnnfi Chemical Rubber Pub. Co., Cleveland, Ohio, pp. 2262,

ure, se mg, enaci y, ion, in oi'ng 2270 2272 2274 1957 5 t percen (g/d) percent Hill, Fibres from Synthetic Polymers, Elsevier Pub.

g2 .3 Co., New York, 1953, pp. 6, 47. 3;? 3 JULIUS FROME, Primary Examiner. 2.1 89 0 J. H. WOO, Assistant Examiner. 

1. A PROCESS FOR TREATING POLYPROPYLENE FILAMENTARY MATERIAL HAVING A MOLECULAR WEIGHT OF AT LEAST 5,000 AND INCLUDING: DRAWING SAID FILAMENTARY MATERIAL TO AT LEAST FOUR TIMES ITS ORIGINAL UNDRAWN LENGTH IN AN ATMOSPHERE OF STEAM AT A TEMPERATURE OF AT LEAST ABOUT 100*C.; AND THEREAFTER HEAT-SETTING SAID FILAMENTARY MATERIAL IN A HOT GASEOUS ATMOSPHERE AT A TEMPERATURE OF FROM BETWEEN ABOUT 120*C. AND THE MELTING POINT OF SAID FILAMENTARY MATERIAL. 